Encapsulation of components and a low energy circuit for hazardous locations

ABSTRACT

Embodiments of the disclosure provide an encapsulated compressor overload, an encapsulated compressor relay start, an encapsulated head pressure control switch and a wiring diagram for a circuit for air conditioning units which prevent gases from being ignited by means of encapsulating sparking components, use of solid-state switching devices, and/or wiring circuits in such a way that open contacts do not contain enough energy to produce a spark capable of igniting the atmosphere.

BACKGROUND

The present disclosure relates generally to air conditioning units foruse in a hazardous environment where flammable gases or vapors mayexist. In particular, the present disclosure relates to air conditioningunits which prevent gases from being ignited by encapsulating sparkingcomponents, using solid-state switching devices, and/or wiring circuitsin such a way that open contacts do not contain enough energy to producea spark capable of igniting the atmosphere.

In many applications, it is necessary to provide air conditioning orrefrigeration systems in locations where flammable gases or vaporsexist. For example, a worker may be surrounded by atmospheric conditionsconducive to danger. An oxygen rich atmosphere might be particularlyconducive to flash fire caused by a stray spark. A similar conditioncould exist in a dust laden atmosphere or in an atmosphere whichincludes flammable vapors. At such locations, it is necessary to provideprotection against the ignition of such flammable gases or vapors, inorder to prevent the occurrence of highly undesired explosions.

In the prior art, explosion-proofing techniques included creating apurged and pressurized system to create a non-hazardous environment, oradding a large cast explosion proof enclosure to contain any undesiredexplosions and placing any sparking devices within the explosion proofenclosure. However, these explosion proof techniques were undulycomplicated and expensive because purge and pressurization devicesrequired shop air, and large cast explosion proof enclosures are bulkyand expensive. Further, these bulky enclosures significantly increasedthe size of the hazardous location rated air conditioners.

SUMMARY OF THE INVENTION

The present disclosure includes a compressor overload for use with airconditioning or refrigeration systems in a hazardous location whereflammable gases or vapors may exist, comprising: a thermal sensor, atleast one overload terminal, a base bracket, a disc, at least one wireconfigured to attach to the at least one overload terminal, andencapsulation material wherein the encapsulation material forms an airtight cover surrounding the compressor overload.

The present disclosure also includes a compressor start relay for usewith air conditioning or refrigeration systems in a hazardous locationwhere flammable gases or vapors may exist, comprising at least one relayterminal, at least one wire coupled onto the at least one relayterminal, and encapsulation material wherein the encapsulation materialforms an air tight cover completely surrounding the compressor startrelay.

The present disclosure includes a wiring circuit for air conditioning orrefrigeration systems in a hazardous location where flammable gases orvapors may exist, comprising a compressor, a transformer, a high energycircuit, a low energy circuit, a solid state relay wherein a firstportion of the solid state relay is configured to connect to the highenergy circuit and a second portion of the solid state relay isconfigured to connect to the low energy circuit, and a line voltage.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a compressor overload.

FIG. 2 is a perspective view of the compressor overload of FIG. 1,showing the compressor overload enclosed in encapsulating material.

FIG. 3 is a schematic wiring diagram of a compressor relay start.

FIG. 4 is a perspective view of the compressor relay start of FIG. 3,showing the compressor relay start enclosed in encapsulating material.

FIG. 5 is a perspective view of a pressure switch with its body wrappedin heat shrink tubing.

FIG. 6 is a schematic wiring diagram of a start circuit, shown as priorart.

FIG. 7 is a schematic wiring diagram of the start circuit of FIG. 6,where a low energy circuit has been added.

DETAILED DESCRIPTION

Before any embodiments of the invention are explained in detail, it isto be understood that the invention is not limited in its application tothe details of construction and the arrangement of components set forthin the following description or illustrated in the following drawings.The invention is capable of other embodiments and of being practiced orof being carried out in various ways. Also, it is to be understood thatthe phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. The use of“including,” “comprising,” or “having” and variations thereof herein ismeant to encompass the items listed thereafter and equivalents thereofas well as additional items. Unless specified or limited otherwise, theterms “connected,” “attached” and “coupled” and variations thereof areused broadly and encompass both direct and indirect mountings,connections, supports, and couplings. Further, “connected,” “attached”and “coupled” are not restricted to physical or mechanical connectionsor couplings.

The following discussion is presented to enable a person skilled in theart to make and use embodiments of the invention. Various modificationsto the illustrated embodiments will be readily apparent to those skilledin the art, and the generic principles herein can be applied to otherembodiments and applications without departing from embodiments of theinvention. Thus, embodiments of the invention are not intended to belimited to embodiments shown, but are to be accorded the widest scopeconsistent with the principles and features disclosed herein. Thefollowing detailed description is to be read with reference to thefigures, in which like elements in different figures have like referencenumerals. The figures, which are not necessarily to scale, depictselected embodiments and are not intended to limit the scope ofembodiments of the invention. Skilled artisans will recognize theexamples provided herein have many useful alternatives and fall withinthe scope of embodiments of the invention.

A compressor overload 10, a compressor start relay 30 and a pressureswitch 50 are each components which can form a part of an airconditioning unit. Any of these components have the potential to createa spark during ordinary use. A spark could lead to an explosion if anyof these components are used in a hazardous location where ignitableconcentrations of flammable gases or vapors may be present. Therefore,it is desirable to encapsulate these components within an air tightmaterial to prevent any potential sparks from mixing with flammablegases or vapors which may exist in the surrounding environment.

FIG. 1 shows one embodiment of a compressor overload 10 having a thermalsensor 12, overload terminals 14, a base bracket 16 and a disc 18. Inthis embodiment, the disc 18 is configured to be coupled to the basebracket 16. The disc 18 can be rotated and locked into the base bracket16. In one embodiment, wires 19 (shown in FIG. 2) can be attached to theoverload terminals 14. The wires 19 can be coupled to the overloadterminals 14 by soldering them onto the terminals 14 or by various otherattachment means known in the art.

A compressor overload 10 can create a spark during operation, whichcould cause a potential explosion in a hazardous environment. Thereforeit is desirable to contain the sparking components of the compressoroverload 10 within an air tight encapsulation material 22 to prevent anypotential sparks from coming into contact with nearby flammable gases orvapors. FIG. 2 shows an embodiment of an encapsulated compressoroverload 20. In this embodiment, components of the compressor overload10 such as the thermal sensor 12, overload terminals 14 and disc 18 arecompletely covered by the encapsulation material 22. The encapsulationmaterial 22 can also cover a portion of the base bracket 16 and aportion of the wires 19.

Various other combinations can be used where different combinations ofcomponents can be enclosed by the encapsulation material 22 as long asthe components which are capable of creating a spark are completelycontained within the encapsulation material 22. The encapsulationmaterial 22 forms an air tight cover surrounding the compressor overload10. In one embodiment the encapsulation material 22 forms a cylindricalcover over the thermal sensor 12, overload terminals 14, base bracket 16and disc 18. However various different shapes can be used for theencapsulation material 22 as long as the shape creates an air tight sealover the potential sparking components. The requirement of an air tightseal also applies where the base bracket 16 and wires 19 extend up to orthrough the encapsulation material 22.

In one embodiment, the bottom surface 24 of the base bracket 16 is notcovered by the encapsulation material 22 and sits flush with theencapsulation material 22. The thermal sensor 12 is located next to thebase bracket 16, which is thermally conductive, to allow the thermalsensor 12 to sense temperature through the bracket 16. The bottomsurface 24 of the base bracket 16 is not covered by any encapsulationmaterial 22 to allow the thermal sensor 12 to sense temperature throughthe base bracket 16.

In one embodiment, the following steps can be used to encapsulate acompressor overload 10. A user can take a compressor overload 10 andattach wires 19 to the overload terminals 14 of the compressor. Thisform of attachment includes but is not limited to direct coupling orsoldering. The base bracket 16 and disc 18 can be cleaned with acleaning agent such as isopropyl alcohol before being coupled together.After cleaning the base bracket 16 and disc 18, the user can rotate thedisc 18 into the base bracket 16 and lock the bracket 16 and disc 18together via various forms of engagement which are known in the art. Inone embodiment, this form of engagement includes a protrusion on thedisc 18 engaging an indentation on the bracket 16.

The user can also substantially or completely cover all the electricallylive parts of the compressor overload 10 with a silicone sealant whichcan be flame resistant. An electrically live part is any part which haselectricity flowing through it. In one embodiment, this flame resistantsealant has a thickness sufficient to meet the UL 94 V-0 minimumflammability rating which is a standard that classifies plasticsaccording to how they burn in various orientations and thicknesses. TheUL 94 V-0 is a plastics flammability standard released by UnderwritersLaboratories of the USA. In one embodiment this minimum thickness is 5.4millimeters. The user can locate or otherwise create a casting or moldin a desired shape for the encapsulation material 22. In the embodimentshown in FIG. 2, the mold has a cylindrical shape but it should beunderstood to one of ordinary skill in the art that various other shapescan be used as well to suit a user's needs.

After obtaining a mold, the user places the compressor overload 10 andany attached wires 19 inside the mold. The user can then pour liquidencapsulation material into the mold to completely encapsulate thecompressor overload 10 and any attached wires 19. After hardening, theencapsulation material 22 creates an air tight seal around thecompressor overload 10 and wires 19 to ensure that any potential sparkis completely contained within the encapsulation material 22 and cannotinteract with any gases or vapors outside the encapsulation material 22.In one embodiment, the encapsulation material 22 can be a polyurethaneresin and/or can have a thickness of one-quarter inch all around. Inanother one embodiment, the encapsulation material 22 can be poured tobe flush with the bottom surface 24 of the base bracket 16.

FIG. 3 shows a wire diagram of one embodiment of a compressor potentialstart relay 30 having relay terminals 32, a first wire 34, a second wire36 and a third wire 38. It should be understood to one of ordinary skillin the art that the compressor start relay 30 is not solely limited tothe use of three wires as shown in FIG. 3, but can use a varying numberof wires. In one embodiment, the first 34, second 36, and third 38 wirescan be attached to individual relay terminals 32. The wires 34, 36, 38can be coupled to the relay terminals 32 by soldering them onto theterminals 14 or by various other attachment means known in the art.

Because a spark can be created during operation of the compressor startrelay 30, it is desirable to contain the sparking components within anair tight encapsulation material 22 to prevent any potential sparks fromcoming into contact with the nearby flammable gases or vapors. FIG. 4shows one embodiment of an encapsulated compressor start relay 40. Inthis embodiment, the compressor start relay 30 and relay terminals 32are completely covered by the encapsulation material 22. Theencapsulation material 22 can also cover a portion of the wires 34, 36,38. The encapsulation material 22 creates an air tight seal over anypotential sparking components. While FIG. 4 shows a boxed shape for theencapsulation material 22, it is understood that any shape which createsan air tight seal over the potential sparking components can be used.The requirement of an air tight seal also applies where the wires 34,36, 38 extend through the encapsulation material 22.

In one embodiment, the following process can be used to encapsulate acompressor start relay 30. A user can take a compressor start relay 30and solder or otherwise attach wires 34, 36, 38 to the individual relayterminals 32 of the start relay 30. The user can also substantially orcompletely cover all the electrically live parts of the compressor startrelay 30 with a flame resistant sealant such as silicone. In oneembodiment, this flame resistant sealant has a thickness sufficient tomeet the UL 94 V-0 minimum flammability rating minimum which in oneinstance can be 5.4 millimeters. Then the user can locate or otherwisecreate a casting or mold in a desired shape for the encapsulationmaterial 22. In the embodiment shown in FIG. 4, the mold has a boxedshape with a flange at one end, but it should be understood to one ofordinary skill in the art that various other shapes could be used aswell.

After obtaining a mold, the user places the compressor start relay 30with wires 34, 36, 38 inside the mold. The user can then pour liquidencapsulation material into the mold to completely encapsulate thecompressor start relay 30 and wires 34, 36, 38. The encapsulationmaterial 22 creates an air tight seal around the compressor start relay30 and wires 34, 36, 38 to ensure that any potential spark is completelycontained within the encapsulation material 22 and cannot interact withany gases or vapors outside the encapsulation material 22. In oneembodiment, the encapsulation material 22 can be a polyurethane resinand can have a thickness of one-quarter inch all around.

FIG. 5 illustrates one embodiment of a pressure switch 50 having a bodyportion 51, a first wire 52 with a first connector 54, a second wire 56with a second connector 58, heat shrink tubing 60, and a third connector62. It should be understood to one of ordinary skill in the art that thepressure switch 50 is not solely limited to the use of two wires asshown in FIG. 5.

Because a spark can be created during operation of the pressure switch50, it is desirable to contain the sparking components within an airtight tube 60 to prevent any potential sparks from coming into contactwith nearby flammable gases or vapors. FIG. 5 shows one embodiment of anencapsulated pressure switch 50. In this embodiment, the body portion 51of the pressure switch 50 is surrounded by tube 60. The tube 60 can alsocover a portion of the wires 52, 56. In one embodiment, a sealantmaterial such as a polyurethane resin can be applied near the first 64and second 66 edges of the tubing to create an air tight seal. Thesealant material creates an air tight seal where the first wire 52,second wire 56, and third connector 62 extend past the first 64 andsecond 66 edges of the tubing 60 respectively. In one embodiment, thesealant material seals the body portion 51, tube 60, first wire 52,second wire 56, and third connector 62 such that these components allrotate together when any of the portion of the body portion 51, tube 60,first wire 52, second wire 56, or third connector 62 is rotated.

In one embodiment, the following process can be used to encapsulate apressure switch 50. A user can take a pressure switch 50 and place heatshrink tubing 60 over a body portion 51 of the pressure switch 50. Theheat shrink tubing 60 should extend past and cover all the componentswithin the body portion 51 which can create a spark. The user can applyheat to the tubing 60 to shrink it down and conform the tubing 60 to thebody portion 51 of the switch 50. The user can also apply a sealantmaterial such as a polyurethane resin near the first 64 and second 66edges of the tubing 60. The sealant material should not exceed the first64 and second 66 edges of the tubing 60 and combined with the tubing 60,should create a completely air tight seal around the body 51 of thepressure switch 50. Creating an air tight seal around the body 51 shouldcompletely seal off the sparking components within the heat shrinktubing 60 which eliminates the risk that these sparking components couldignite nearby flammable gases or vapors present in a hazardous location.

By sealing off the sparking components 10, 30, 50 individually, a useravoids having to use alternative safeguards such as a purged andpressurized air system to prevent hazardous outside air from coming intocontact with a spark. A purged and pressurized air system can be bothcomplicated and expensive. Similarly, a user also avoids having to usean alternative such as building out a large cast explosion-proofenclosure and placing all of the sparking components within thisenclosure. Placing all of the potential sparking components in a singleenclosure requires reconfiguring the overall size and shape of the airconditioner to accommodate having all the sparking components in onecentral location.

The present disclosure allows a user to seal off each sparking componentindividually and therefore allows a user to avoid having to install apurged and pressurized air system, thus enabling the user to maintainthe same overall size and shape of a non-hazardous location airconditioner. This results in a lower overall cost and creates a compactself-contained cooling device.

Another way to provide protection against the potential ignition offlammable gases or vapors is to wire the air conditioner to make use ofa low energy circuit where the energy is a function of the voltage andcurrent in a circuit. The low energy circuit is sufficiently low inenergy such that it does not contain enough energy to produce a sparkcapable of igniting the surrounding atmosphere.

FIG. 6 illustrates a wiring diagram of an air conditioning unitaccording to the prior art. In this air conditioning unit, the wiringfor the compressor 70 uses high voltage throughout the entirety of itscircuit and thus is powered by a high energy circuit. The compressor 70is directly connected to a compressor start relay 76, which in turn isconnected to a compressor start capacitor 78. The compressor startcapacitor 78 is connected to the compressor 70 which is also wired to amechanical contactor 80. The mechanical contactor 80 is directlyconnected to the line voltage 74. Thus, the compressor 70 is connectedto the line voltage 74 and uses high voltage throughout its circuit.Because the compressor wiring uses high voltage throughout its circuit,there is a potential for a spark to be created in the compressor startrelay 76 between connection points 82, 84. To remove the potential for aspark, the compressor wiring can be reconfigured as shown in FIG. 7.

FIG. 7 illustrates a wiring diagram of one embodiment of an airconditioning unit where a low energy circuit has been introduced intothe compressor wiring. That same principles discussed below would alsoapply to wiring for a refrigeration unit. In this circuit, the wiringfor the compressor 170 uses both high voltage and low voltage. Thecompressor 170 is connected to a first solid state relay 188 and acompressor start relay 176. The compressor start relay 176 is connectedto a second solid state relay 192. A first side 190 of the second solidstate relay 192 is connected to the secondary side of the step downtransformer 172 and thus operates on low voltage. However, a second side194 of the second solid state relay 192 is wired to a start capacitor178, which is connected to line voltage 175, and therefore it operateson high voltage. The line connections between the connection points 182,184 of the compressor start relay 176 and the first side 190 of thesecond solid state relay 192 all use low voltage and therefore operateon a low energy circuit.

The second side 194 of the second solid state relay 192 is connected tothe start capacitor 178, which in turn is connected to the line voltage175. Therefore, the second side 194 of the second solid state relay 192operates on high voltage and a high energy circuit because it is poweredby line voltage 175.

By introducing a low energy circuit, the spark potential in thecompressor start relay 176 between connection points 182, 184 has beenremoved because these connection points 182, 184 are now wired to thesecondary side of the step down transformer 172. In one embodiment, theline voltage 174 on the primary side of the transformer is 115 volts andthe low voltage on the secondary side of the transformer 172 is 24volts. Thus the connection points 182, 184 are now wired using lowvoltage which does not contain enough energy to produce a spark capableof igniting the gases and vapors in the surrounding hazardousenvironment.

In one embodiment, an overcurrent relay 196 is added to the circuit inorder to provide protection against excessive currents. To furthereliminate the potential for a spark, the mechanical contactor 80 (shownin FIG. 6) has been replaced by a solid state relay 188 which does notcreate a spark potential. Thus, by introducing a low energy circuit andreplacing the mechanical contactor 80 with a solid state relay 188, thepotential for sparking has been significantly reduced. The low energycircuit eliminates the need for any type of encapsulation,explosion-proof enclosure or purge and pressurization device.

It will be appreciated by those skilled in the art that while thedisclosure has been described above in connection with particularembodiments and examples, the disclosure is not necessarily so limited,and that numerous other embodiments, examples, uses, modifications anddepartures from the embodiments, examples and uses are intended to beencompassed by the claims attached hereto.

The invention claimed is:
 1. An encapsulated compressor overload for usewith air conditioning or refrigeration systems in a hazardous locationwhere flammable gases or vapors may exist, the encapsulated compressoroverload comprising: a compressor overload comprising: a thermal sensor;at least one overload terminal each attached to one of one or morewires; a thermally conductive base bracket located next to the thermalsensor to allow the thermal sensor to sense temperature through the basebracket; and a disc coupled to the base bracket; and encapsulationmaterial forming an air tight cover surrounding the compressor overloadand allowing the one or more wires and the base bracket to extendthrough the air tight cover, such that sparks created by the compressoroverload are completely contained within the encapsulation material andprevented from coming into contact with the flammable gases and vapors.2. The encapsulated compressor overload of claim 1 wherein the basebracket comprises a bottom surface which is not covered by theencapsulation material and is flush with the encapsulation material. 3.The encapsulated compressor overload of claim 1 wherein theencapsulation material is a polyurethane resin and is about one-quarterinch thick.
 4. The encapsulated compressor overload of claim 1 whereinall components of the compressor overload which have the ability tobecome electrically live are substantially covered with a siliconesealant.
 5. The encapsulated compressor overload of claim 4 wherein thesilicone sealant has a minimum thickness sufficient to meet the minimumflammability rating requirements of UL 94 V-0.
 6. An apparatus foradapting a non-hazardous location air conditioner for use in anenvironment in which flammable gases or vapors are present, theapparatus comprising: an encapsulated compressor overload electricallyconnected to a compressor of the air conditioner, the encapsulatedcompressor overload comprising: a compressor overload comprising: one ormore components capable of sparking during operation; and a basebracket; and a first encapsulation material forming an air tight coversurrounding the one or more components of the compressor overload, suchthat sparks created by the compressor overload are completely containedwithin the first encapsulation material and prevented from coming intocontact with the flammable gases and vapors, the base bracket of thecompressor overload extending through the first encapsulation material.7. The apparatus of claim 6, wherein a bottom surface of the basebracket is not covered by and sits flush with the first encapsulationmaterial, wherein the base bracket is thermally conductive, and whereinthe one or more components of the compressor overload include a thermalsensor located next to the base bracket and sensing temperature throughthe base bracket.
 8. The apparatus of claim 6, wherein the one or morecomponents of the compressor overload include an overload terminalattached to a wire that extends through the first encapsulationmaterial.
 9. The apparatus of claim 6, further comprising anencapsulated compressor start relay electrically connected to thecompressor of the air conditioner, the encapsulated compressor startrelay comprising: a compressor start relay having a plurality of relayterminals each attached to a corresponding wire of a plurality of wires;and a second encapsulation material forming an air tight covercompletely surrounding the compressor start relay and allowing theplurality of wires to extend through the air tight cover, such thatsparks created by the compressor start relay are completely containedwithin the second encapsulation material and prevented from coming intocontact with the flammable gases and vapors.
 10. The apparatus of claim9, further comprising an encapsulated pressure switch in electricalcommunication with the compressor of the air conditioner, theencapsulated pressure switch comprising: a pressure switch having one ormore components capable of sparking during operation; an air tight tubesurrounding the one or more components of the pressure switch and havinga first edge and a second edge; and a sealant material applied to eachof the first edge and the second edge, creating an air tight seal aroundthe one or more components of the pressure switch that prevents sparksof the pressure switch from coming into contact with the flammable gasesand vapors.
 11. The apparatus of claim 10, wherein the one or morecomponents of the pressure switch include a body portion surrounded bythe tube, the pressure switch further comprising: a connector extendingthrough the sealant material at the first edge of the tube; and one ormore wires extending through the sealant material at the second edge ofthe tube.
 12. The apparatus of claim 10, wherein each of theencapsulated compressor overload, the encapsulated compressor startrelay, and the encapsulated pressure switch is individually sealed offfrom each other sparking components of the air conditioner.
 13. Theapparatus of claim 9, wherein one or both of the first encapsulationmaterial and the second encapsulation material are a polyurethane resin.14. The apparatus of claim 9, wherein one or both of the firstencapsulation material and the second encapsulation material are aboutone-quarter inch thick.